Results by Quarter (Unaudited) Results by Quarter (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011		Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 2,072.6	$ 1,726.5		$ 1,740.7	$ 1,474.8	$ 2,005.2	$ 1,553.4	$ 1,611.7	$ 1,337.0	$ 7,014.6	$ 6,507.3	$ 6,007.4
Salaries and related expenses	1,138.3	1,088.0		1,095.7	1,080.1	1,139.6	1,007.1	991.0	979.3	4,402.1	4,117.0	3,961.2
Office and general expenses	548.8	465.5		470.8	439.2	533.3	444.7	442.9	416.8	1,924.3	1,837.7	1,700.3
Restructuring and other reorganization-related charges (reversals), net	0.2	(0.2)		0.2	0.8	1.6	1.4	0.6	0.3	1.0	3.9	4.6
Operating (loss) income	385.3	173.2		174.0	(45.3)	330.7	100.2	177.2	(59.4)	687.2	548.7	341.3
Other (expense) income, net	13.9	137.1	[1]	5.3	(6.1)	17.6	(3.1)	(2.1)	0.5	150.2	12.9	11.7
Total (expenses) and other income	(14.9)	113.9	[1]	(18.1)	(29.7)	(10.5)	(31.0)	(31.0)	(25.6)	51.2	(98.1)	(108.9)
(Benefit of) provision for income taxes	93.7	70.4		47.6	(21.5)	98.9	24.4	63.3	(15.3)	190.2	171.3	90.1
Net (loss) income	278.3	217.5	[1]	108.9	(53.2)	222.8	45.6	83.1	(70.3)	551.5	281.2	143.4
Net (loss) income available to IPG common stockholders	259.0	208.1	[1]	101.7	(48.1)	195.0	42.4	105.3	(71.5)	520.7	271.2	93.6
Earnings Per Share [Abstract]
Basic	$ 0.58	$ 0.45		$ 0.21	$ (0.10)	$ 0.41	$ 0.09	$ 0.22	$ (0.15)	$ 1.12	$ 0.57	$ 0.20
Diluted	$ 0.50	$ 0.40		$ 0.19	$ (0.10)	$ 0.36	$ 0.08	$ 0.15	$ (0.15)	$ 0.99	$ 0.47	$ 0.19
Dividends declared per common share	$ 0.06	$ 0.06		$ 0.06	$ 0.06	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.24	$ 0.00	$ 0.00
Gain recorded on sale of portion of Facebook		$ 132.2								$ 132.2	$ 0	$ 0

[1] The three months ended September 30, 2011, includes a pre-tax gain of $132.2 related to the sale of approximately half of our holdings in Facebook, Inc.